The church teachers that the male climax must occur only though sexual intercourse, which I accept. My question is for the elderly, such as a couple in their 70's which reasonably have no chance for pregnancy.

If they do not have medical or health conditions that prevent them from having intercourse, it is sinful for them to climax through means other than intercourse? Does the Church believe they are committing a sin so serious that it potentially qualifies to be a mortal sin?

Let's take this one step further... Medical doctors specifically recommended that men with prostate problems should "drain the prostate" (ejaculate) frequently. Would the Church condemn having the married couple in thier 70's fondle each other to climax if they could not have intercourse due the their physical condition even if it was to help the male follow his doctor's medical course of treatment to preserve life?

Human genital activity has a context. This context is that of expressing physically the wedding vows made at the altar. This context does not change simply because the couple has advanced in years. The Catechism of the Catholic Church (2352) defines masturbation as “the deliberate stimulation of the genital organs in order to derive sexual pleasure.

Therefore, this does not rule out such stimulation for medical reasons where the context is medical treatment. But it does rule it out as a substitute for normal sexual relations where the context is stated above. Such masturbation is considered to be “an intrinsically and gravely disordered action.” This means it’s seriously (mortally) sinful. The elderly are allowed to attempt normal sexual relations and experience such sexual pleasure even if they are not capable of fully completing the act—because here they are acting within the proper context of marital intercourse.